U.S. patent number 6,718,764 [Application Number 10/184,492] was granted by the patent office on 2004-04-13 for system and method for microstructure positioning using metal yielding.
This patent grant is currently assigned to Zyvex Corporation. Invention is credited to Aaron Geisberger, Niladri Sarkar.
United States Patent |
6,718,764 |
Sarkar , et al. |
April 13, 2004 |
System and method for microstructure positioning using metal
yielding
Abstract
A system and method of adjusting the power off positioning of a
microactuator is disclosed. The microactuator has a first power off
position and comprises a bimorph component. The bimorph comprises
at least two materials, wherein the materials have different
thermal expansion characteristics. When heated, the bimorph
component of the microactuator bends due to asymmetric thermal
expansion of the materials. If one of said materials is forced
beyond a yield point, then when cooled, the actuator assumes a
second power off position. The microactuator maintains the second
power off position due to stress in the bimorph, which is induced
by forcing the material beyond its yield point.
Inventors: |
Sarkar; Niladri (Brossard,
CA), Geisberger; Aaron (Plano, TX) |
Assignee: |
Zyvex Corporation (Richardson,
TX)
|
Family
ID: |
32041606 |
Appl.
No.: |
10/184,492 |
Filed: |
June 28, 2002 |
Current U.S.
Class: |
60/527;
60/528 |
Current CPC
Class: |
B81B
3/0024 (20130101); G02B 6/4226 (20130101); B81B
2201/032 (20130101) |
Current International
Class: |
B81B
3/00 (20060101); G02B 6/42 (20060101); F01B
029/10 () |
Field of
Search: |
;60/527,528,529 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
US. patent application Ser. No. 09/932,489, Ellis et al. .
Zhang, Yanhang et al., "Stress Relaxation of Gold/Polysilicon
Layered MEMS Microstructures Subjected to Thermal Loading,"
Proceedings of 2001 ASME IMECE 2001, pp. 1-8. .
Zou, Jun et al., "Plastic Deformation Magnetic Assembly (PDMA) of
3D Microstructures: Technology Development and Application,"
Transducers '01, Eurosensors XV, 2001, 4 pages..
|
Primary Examiner: Nguyen; Hoang
Attorney, Agent or Firm: Haynes and Boone, LLP
Claims
What is claimed is:
1. A method of adjusting the power off positioning of a
microactuator having a first power off position, comprising:
providing a bimorph component of said microactuator, the bimorph
comprising at least two materials, wherein the materials have
different thermal expansion characteristics; heating the bimorph
component of the microactuator until one of said materials is
forced beyond a yield point; and allowing said bimorph component to
cool and to assume a second power off position, wherein said
microactuator maintains said second power off position due to
stress in said bimorph, the stress induced by forcing said material
beyond said yield point.
2. The method of claim 1 further comprising: attaching a
microdevice to said microactuator so that said microdevice moves
when power is applied to said microactuator.
3. The method of claim 1 wherein said heating step further
comprises: heating by passing an electric current through said
bimorph component.
4. The method of claim 1 wherein said heating step further
comprises: using a laser to heat said bimorph component.
5. The method of claim 1 wherein said material forced beyond a
yield point is a metal.
6. The method of claim 1 wherein said bimorph is comprised of a
metal and polysilicon.
7. The method of claim 1 further comprising: moving the
microactuator from said second power off position by heating said
bimorph.
8. The method of claim 7 wherein said microactuator is moved from
said second power off position to said first power off position,
and wherein said microactuator must be heated to maintain said
first power off position.
9. The method of claim 1 further comprising: heating said bimorph a
second time until said material passes said yield point a second
time; and allowing said bimorph component to cool and to assume a
third power off position, wherein said microactuator maintains said
third power off position due to stress in said bimorph, the stress
induced by forcing said material beyond said yield point.
10. The method of claim 9 further comprising: cycling said bimorph
between heating and cooling cycles until said microactuator
maintains a desired power off position.
11. A microactuator device comprising: an actuator arm having at
least two materials bonded together to form a bimorph, the
materials having different thermal expansion coefficients, the
actuator arm having a first end and a second end, the first end
attached to a fixed structure and the second end adapted to receive
a microcomponent, wherein one of the at least two materials
comprises a residual stress, the residual stress induced by heating
the one of the at least two materials until forced beyond a yield
point.
12. The microactuator of claim 11 further comprising: electrical
contacts adapted for providing electrothermal heating to said
actuator arm.
13. The microactuator of claim 11 wherein said actuator arm is
positioned a sufficient distance above a substrate to allow said
actuator arm to bend without obstruction under increased
temperature conditions.
14. The microactuator of claim 11 wherein one of said materials is
a metal.
15. The microactuator of claim 11 wherein one of said materials is
polysilicon.
16. The microactuator of claim 11 wherein said microcomponent is an
optical receiver.
17. The microactuator of claim 11 wherein said microcomponent is an
optical transmitter.
18. The microactuator of claim 11 wherein said microcomponent is a
capacitor plate and wherein said actuator arm is positioned to
adjust a capacitance.
19. The microactuator of claim 11 wherein said microcomponent is an
inductor and wherein said actuator arm is positioned to reduce
coupling between the inductor and a substrate.
20. A rotary actuator comprising: a plurality of cascaded coupled
beams, each of said beam having a first arm and a second arm, said
plurality of cascaded beams disposed in at least one substantially
planar folded serpentine array structure such that a first arm of a
first adjacent beam is rigidly joined to a second arm of a second
adjacent beam in said serpentine array structure; wherein said
first arm of each beam is operable when activated to deflect in a
first direction out of a plane of said substantially planar folded
serpentine array structure; wherein said second arm is operable
when activated to remain undeflected; an initial beam and a final
beam in said serpentine array structure each having a terminal end
not joined together with an adjacent beam; said folded serpentine
array structure operable when activated to rotate said final
terminal end relative to said initial terminal end through an angle
of rotation substantially proportional to the sum of the
deflections of all of said cascaded coupled beams in said folded
serpentine array structure; and wherein said first arm of at least
one of said beams is a bimorph having an initial configuration that
is modified to a second configuration when heated beyond a yield
point.
21. The rotary actuator of claim 20 wherein said angle of rotation
is greater than ninety degrees.
22. The rotary actuator of claim 20 wherein said initial terminal
end is attached to a substrate using a technique selected from the
group consisting of permanent anchoring and flexible tethering.
23. The rotary actuator of claim 20 wherein said initial terminal
end is releasably fastened to a substrate.
24. The rotary actuator of claim 20 further operable to erect said
rotary actuator off of a substrate.
25. The rotary actuator of claim 20 further comprising an inductive
or capacitive element coupled to said beams.
26. The rotary actuator of claim 20 wherein said final terminal end
is coupled to a payload region and wherein said actuator is
operable to rotate a payload on said payload region.
27. The rotary actuator of claim 26 wherein said payload is
selected from the group consisting of microcomponents, mirrors, and
pick-and-place devices.
28. The rotary actuator of claim 20 wherein said lengths of said
arms are substantially uniform.
29. The rotary actuator of claim 20 wherein said arms are staggered
in length.
30. The rotary actuator of claim 20 wherein said beams are operable
to be thermally activated.
31. The rotary actuator of claim 30 wherein said beams are operable
to be thermally activated using a method selected from the group
consisting of oven heating, laser heating, conductive heating, and
resistive joule heating.
32. The rotary actuator of claim 20 wherein said bimorph is
comprised of a metal and polysilicon.
33. A method of rotary actuation of an actuator comprising the
steps of: coupling a plurality of beams together in at least one
substantially planar folded serpentine array structure such that
adjacent beams in said serpentine array structure are substantially
parallel in length to one another, each beam comprising a first arm
and a second arm, wherein said beams are rigidly joined together
such that the first arm of a first adjacent beam is rigidly joined
to a second arm of a second adjacent beam in said serpentine array
structure, wherein said first arm of at least one of said beams is
a bimorph having an initial configuration that is modified to a
second configuration when heated beyond a yield point, and
activating said beams such that said first beams deflect in a first
direction in a plane substantially perpendicular with said
substantially planar folded serpentine array structure and
substantially parallel with said lengths of said beams and such
that said second beams remain undeflected, such that a final
terminal end is rotated relative to an initial terminal end through
an angle of rotation substantially proportional to the sum of the
deflections of all of said first beams in said folded serpentine
array structure.
34. The method of claim 33 wherein said beams are thermally
activated.
35. The method of claim 34 wherein said beams are thermally
activated by a method selected from the group consisting of oven
heating, laser heating, conductive heating, and resistive joule
heating.
36. The method of claim 34 wherein said thermal activation causes
differential thermal expansion in materials comprising said
bimorph.
37. The method of claim 33 wherein said bimorph comprises at least
two materials and further comprising: forcing said bimorph beyond a
yield point of one of said materials.
38. The method of claim 33 wherein said activating step causes an
angle of rotation greater than ninety degrees.
39. The method of claim 33 wherein said activating step causes said
actuator to self erect off of a substrate.
40. The method of claim 33 further comprising: rotating a payload
region attached to said final terminal end.
41. The method of claim 33 wherein said final terminal end is
coupled to a payload region operable to carry a payload.
42. The method of claim 33 wherein said beams in said serpentine
array structure are connected electrically in series with one
another.
43. The method of claim 41 comprising a second said serpentine
array structure coupled to said payload region of a first said
serpentine array structure.
44. The method of claim 43 wherein said beams in said first and
said second said serpentine array structures are electrothermally
activated by electric current in two interwoven current paths.
45. The method of claim 44 wherein said electrical currents in said
serpentine array structures are independently variable.
46. The method of claim 33 operable to produce rotary motion about
a combination of rotational axes.
47. The method of claim 33 further comprising components selected
from the group consisting of rotary tweezers, mirrors, optical
alignment means, beam steering devices, optical scanning devices,
micro-surgical devices, and microelectromechanical structure
manipulation devices.
48. The method of claim 33 further comprising one or more capacitor
plates coupled to said beams.
49. The method of claim 33 further comprising one or more inductors
coupled to said beams.
Description
TECHNICAL FIELD
This invention is related to positioning devices in
microelectromechanical systems (MEMS) and, more particularly, to
using a bimorph actuator that has been modified to affect the power
off position of the positioning device.
BACKGROUND OF THE INVENTION
MicroElectroMechanical ("MEM") devices comprise integrated
micromechanical and microelectronic devices. The term
"microcomponent" will be used herein generically to encompass
microelectronic components, micromechanical components, as well as
MEMs components. The advances in microcomponent technology have
resulted in an increasing number of microcomponent applications.
Accordingly, a need often arises for precise positioning of
microcomponent devices. For example, it is often desirable to
position a microcomponent in alignment with a target position. For
instance, for certain applications it may be desirable to align a
microcomponent with another device. Because of the small size of
microcomponents, they often require very precise positioning (e.g.,
precise alignment with another device). For example, in some cases
a misalignment of only a few microns may be unacceptable. In fact,
in some cases the size of the microcomponent being aligned may be
only a few microns. Also, microcomponents present particular
difficulty in handling and positioning operations.
Plastic deformation of single composition MEM devices is known. For
example, U.S. Pat. No. 6,261,494, entitled METHOD OF FORMING
PLASTICALLY DEFORMABLE MICROSTRUCTURES, the disclosure of which is
incorporated herein by reference herein, teaches a method of
plastically deforming MEM structures. Copending U.S. patent
application Ser. No. 09/932,489, filed Aug. 17, 2001, and entitled
SYSTEM AND METHOD FOR PRECISE POSITIONING OF MICROCOMPONENTS, the
disclosure of which is hereby incorporated by reference herein,
teaches deforming microactuators to fix the position of
microcomponents.
Stress relaxation in bimorph microstructures is also known. For
example, in the article entitled "Stress Relaxation of
Gold/Polysilicon Layered MEMS Microstructures Subjected to Thermal
Loading," by Zhang and Dunn, stress relaxation is studied for gold
within a gold/polysilicon bimorph device. Creep may occur at
elevated temperatures and may cause deformation if the bimorph is
exposed to an elevated temperature over a period of time.
Accordingly, yielding mechanisms in some materials are time and
temperature dependent as well as stress dependent.
Microcomponents are commonly implemented in the field of
optoelectronics. Generally, when coupling optoelectronic
components, alignment is very important. That is, alignment of
optoelectronic components is often critical for proper operation of
an optoelectronic device. A relatively slight misalignment of
optical components may drastically alter an optical device's
performance. For example, accurate alignment of components is often
important for ensuring proper propagation of an optical signal
to/from/within an optoelectronic device. For instance,
optoelectronic modules, such as optoelectronic receivers and
optoelectronic transmitters commonly require proper alignment of
microcomponents therein for proper operation. In general, proper
alignment is desired to minimize the amount of attenuation within
such optoelectronic devices.
One microcomponent that often requires proper alignment is an
optical fiber. For example, in an optoelectronic receiver, a fiber
is aligned with an optical detector, typically a PIN photodiode.
Very large fibers may have light-guiding cores with a diameter of
approximately 1 millimeter (mm) or 1000 microns (.mu.m), but such
fibers are rarely used in communications. Standard glass
communication fibers have cladding diameter of 125 .mu.m and
light-guiding cores with diameter of approximately 8 to 62.6 .mu.m.
Proper alignment of the end of the optical fiber (which may be
referred to as the "fiber pigtail") with the optical detector is
important to ensure that a light signal is properly received by the
optical detector. Similarly, in an optoelectronic transmitter, an
optical fiber is aligned with a light source, such as a
light-emitting diode (LED) or laser diode. Proper alignment of the
end of the optical fiber with the light source is important to
ensure that a light signal is properly communicated from the light
source to the optical fiber.
The difficulty in achieving proper alignment of optical fiber is
often increased because of variances in the size of fiber core
diameters. For example, typical commercial graded-index fiber
commonly specify a 50 .mu.m nominal fiber core diameter that may
vary within a tolerance of .+-.3 .mu.m. Also, alignment/positioning
of the light-guiding core within the sleeve of a fiber optic cable
often varies (i.e., the core is not always centered within the
sleeve), thereby further increasing the difficulty of properly
designing a fiber with another optoelectronic device.
Various techniques have been developed for handling and positioning
microcomponents, such as optical fibers. According to one
technique, a high-precision, external robot is utilized to align
microcomponents within devices. However, such external robots are
generally very expensive. Additionally, external robots typically
perform microcomponent alignment in a serial manner, thereby
increasing the amount of time required for manufacturing
microcomponent devices. That is, such robots typically perform
alignment for one component at a time, thereby requiring a serial
process for assembling microcomponents utilizing such a robot.
According to another technique, microactuators, such as
electrothermal actuators, may be utilized to align microcomponents,
such as optical fibers. For example, microactuators may be
integrated within a device to align microcomponents within the
device. Accordingly, use of such microactuators may avoid the cost
of the above-described external robot. Also, if implemented within
a device, the microactuators may enable parallel alignment of
microcomponents. That is, multiple devices may have alignment
operations performed by their respective microactuators in
parallel, which may reduce the amount of time required in
manufacturing the devices. Examples of techniques using
microactuators integrated within a device to perform alignment of
an optical fiber are disclosed in U.S. Pat. Nos. 6,164,837 and
5,602,955, the disclosures of which are hereby incorporated by
reference herein.
Once a desired position is obtained for a microcomponent (e.g.,
alignment with another device) using either of the above
techniques, such microcomponent may have its position fixed in some
manner such that it maintains the desired position. Various
techniques have been developed for fixing the position of
microcomponents. According to one technique, an epoxy may be used
to fix the position of a microcomponent. In another technique a low
melting point bonding material, such as solder, may be used to fix
the position of a microcomponent. Exemplary techniques that use
solder to fix the position of an optical fiber are disclosed in
U.S. Pat. No. 6,164,837, U.S. Pat. No. 5,692,086, and U.S. Pat. No.
5,745,624, the disclosures of which are hereby incorporated by
reference herein.
According to another technique, an "active" alignment device may be
utilized to fix the position of a microcomponent. Such an alignment
device is "active" in the sense that electrical power has to be
maintained in order to fix the alignment of a microcomponent. For
example, in certain implementations that use microactuators
integrated within a device to perform alignment of microcomponents,
power to such microactuators must be maintained in order to
maintain (or fix) the position of the microcomponents being
aligned.
Plastic deformation micro-assembly has been demonstrated using
Plastic Deformation Magnetic Assembly (PDMA), such as in the
article entitled "Plastic Deformation Magnetic Assembly (PDMA) of
3D Microstructures: Technology Development and Application," by J.
Zou, J. Chen and C Liu. However, PDMA technology can only be
deformed to one position (i.e. unidirectional) and cannot be
adjusted after the assembly step. Also, it requires the use of an
external magnetic field and magnetic materials in the actuator
itself.
SUMMARY OF THE INVENTION
The present invention is directed to a system and method in which a
bimorph is used in a microelectromechanical actuator to modify the
power off positioning of the actuator. The bimorph is comprised of
two materials that are bonded together, each material having a
different thermal expansion coefficient so that they expand at
different rates when the temperature is increased. The temperature
may be increased by applying a current to the bimorph or by
applying an external heat source, such as a laser, to the
bimorph.
As the bimorph is heated, the materials expand at different rates,
thereby causing the bimorph to bend. Normally, when the heat source
is removed, the bimorph will return to its original state. However,
when the bimorph is heated such that the stress in one of the
materials increases beyond the yield point, the bimorph is
plastically deformed so that it does not return to its initial
state after the heat source is removed. Instead, because of
residual stress that is present in the material that was
plastically deformed, when the heat source is removed, the bimorph
is forced to bend in a direction opposite to the bending due to
expansion. Typically, the material that has a higher thermal
expansion coefficient will reach its yield point first and,
therefore, will be plastically deformed.
As a result of the residual stress in the plastically deformed
material, the bimorph assumes a new initial state. When the bimorph
forms part of a microelectromechanical actuator, the microactuator
assumes a new initial or power off state. Additionally, although
the power off state of the microactuator may be modified from an
initial position using the method of the present invention, the
microactuator can still be moved by heating and thermal
expansion.
The present invention has application in many areas, such as the
telecommunications and fiber areas discussed above. Other
applications, such as in microwave circuits, are also possible. For
example, the deformable structures disclosed herein may be used to
place inductors at a 90 degree angle to the substrate. In other
applications, the invention can be used to adjust the positioning
of capacitive plates.
The foregoing has outlined rather broadly the features and
technical advantages of the present invention in order that the
detailed description of the invention that follows may be better
understood. Additional features and advantages of the invention
will be described hereinafter which form the subject of the claims
of the invention. It should be appreciated by those skilled in the
art that the conception and specific embodiment disclosed may be
readily utilized as a basis for modifying or designing other
structures for carrying out the same purposes of the present
invention. It should also be realized by those skilled in the art
that such equivalent constructions do not depart from the spirit
and scope of the invention as set forth in the appended claims. The
novel features which are believed to be characteristic of the
invention, both as to its organization and method of operation,
together with further objects and advantages will be better
understood from the following description when considered in
connection with the accompanying figures. It is to be expressly
understood, however, that each of the figures is provided for the
purpose of illustration and description only and is not intended as
a definition of the limits of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention,
reference is now made to the following descriptions taken in
conjunction with the accompanying drawings, in which:
FIG. 1A is an exemplary bimorph of the present invention in an
initial state;
FIG. 1B is the bimorph of FIG. 1A in a state of elevated
temperature;
FIG. 1C is the bimorph of FIG. 1A after exposure to the elevated
temperature of FIG. 1B;
FIG. 1D is the bimorph of FIG. 1C at an elevated temperature
state;
FIG. 2A is a top view of a bimorph actuator according to one
embodiment of the present invention;
FIG. 2B is a side view of the bimorph actuator of FIG. 2A;
FIG. 2C is a side view of the bimorph actuator under elevated
temperature conditions;
FIG. 2D is a side view of the bimorph actuator after it has been
heated beyond its yield point in FIG. 2C;
FIG. 3A is a rotary actuator according to one embodiment of the
present invention;
FIG. 3B is the rotary actuator of FIG. 3A with power applied so
that the rotary actuator moves from an original configuration;
FIG. 3C is the rotary actuator of FIG. 3A in a modified initial
configuration after being plastically deformed;
FIG. 4 is an exemplary deformable self-erecting structure that uses
embodiments of the present invention;
FIG. 5A is an alternative embodiment of a microactuator according
to one embodiment of the invention;
FIG. 5B is the microactuator of FIG. 4A when power is applied to
the microactuator;
FIG. 5C illustrates a new power off configuration of the
microactuator of FIG. 4A after the microactuator has been pushed
beyond a yield point; and
FIG. 6 is a flowchart illustrating a method of plastically
deforming a microactuator according to one embodiment of the
invention.
DETAILED DESCRIPTION
FIG. 1A is an exemplary bimorph 100a that is constructed of two
materials 101, 102 that are bonded together. The materials may be
bonded together using any appropriate method or process. Each
material, 101 and 102, has a respective thermal expansion
coefficient, .alpha..sub.1 and .alpha..sub.2. Preferably, the
thermal expansion coefficients .alpha..sub.1 and .alpha..sub.2 are
sufficiently different so that materials 101 and 102 expand at
different rates. In the embodiment illustrated herein,
.alpha..sub.1 is greater than .alpha..sub.2 (i.e. .alpha..sub.1
>.alpha..sub.2) so that material 101 expands at a faster rate
than material 102 when both are exposed to the same temperature
increase. FIG. 1A represents an initial configuration of bimorph
100a at an initial temperature, such as room temperature or an
expected operating temperature. Bimorph 100a is initially oriented
so that it is essentially parallel to the x axis of FIG. 1A.
FIG. 1B illustrates changes to bimorph 100a under elevated
temperature conditions. Bimorph 100a, after being heated, is forced
to bend in the direction of the negative y axis due to the higher
thermal expansion coefficient, .alpha..sub.1, of material 101. As
materials 101 and 102 are heated, each material attempts to expand
linearly along the x axis. Top material 101 expands at a faster
rate and, therefore, to a longer length than material 102 due to
its higher thermal expansion coefficient. As a result, as
illustrated in FIG. 1B, bimorph 100b bends or deforms downward in
the negative y axis direction.
The extent of the deformation depends upon the amount of heat
applied to bimorph 100b. As more heat is applied, bimorph 100b
bends further downward as material 101 expands further than
material 102. Heating may be accomplished in any manner practical
to the application. For example, material 101 and 102 may be heated
by passing an electrical current through the bimorph or by applying
an external heat source, such as laser energy, to the bimorph.
If the temperature is elevated high enough, the difference in
thermal expansion coefficients between the two materials creates
such a high stress in material 101 that it will actually yield. At
the yield point material 101 will plastically deform on itself
instead of moving bimorph 100b further.
FIG. 1C illustrates the configuration of bimorph 100b when it is
cooled after being heated beyond the yield point of material 101.
Thermal expansion deforms material 101 in FIG. 1B and then, as
bimorph 100b cools down to the initial temperature, the bimorph
moves to the position 100c illustrated in FIG. 1C. Bimorph 100c has
been plastically deformed due to the elevated temperature in FIG.
1B. When the bimorph is cooled, materials 101 and 102 contract.
Material 102 attempts to assume its original configuration as
illustrated in FIG. 1A. However, because material 101 has been
plastically deformed, materials 101 and 102 assume the shape of
bimorph 100c.
Material 101 in FIG. 1C is still under stress due to being
plastically deformed at the elevated temperature. Material 102, in
FIG. 1C, is forced to bend due to the residual stress in material
101. As a result, the initial, power-off or at-rest condition of
the bimorph has been changed from the original condition
illustrated by bimorph 100a to the power off state 100c.
If bimorph 100c is heated, materials 101 and 102 will again expand
and bimorph 100c will again bend downward due to the higher thermal
expansion coefficient of material 101. In FIG. 1D, bimorph 100d
represents the changes to bimorph 100c under elevated temperature
conditions. Bimorph 100d has been heated and, in the exemplary
illustration, expansion forces bimorph 100d to assume a
substantially flat position that is similar to the initial
condition of bimorph 100a. However, when the elevated temperature
is removed, bimorph 100d will cool and return to the new initial
condition illustrated by bimorph 100c in FIG. 1C.
Comparing FIGS. 1A and 1D, bimorphs 100a and 100d are in the same
position, however, bimorph 100d must be heated to assume this
position, while bimorph 100a is at an initial, non-elevated
temperature. On the other hand, in FIGS. 1A and 1C, although
bimorphs 100a and 100c are at the same initial temperature, bimorph
100c has assumed a new initial condition compared to the original
positioning of bimorph 100a due to plastic deformation. These
changes can be put to practical use in actuator or positioning
elements in microelectromechanical (MEM) structures.
Using the method described above, a MEM actuator may be permanently
plastically deformed to adjust its initial condition or position.
Such adjustments may be performed iteratively to fine tune the
initial positioning of the MEM structure. Materials 101 and 102 may
be any plastically deformable material, such as nickel, gold,
chrome, aluminum, metal, polysilicon or the like. The plastically
deformable material, 101, 102, may be deposited by electroplating,
etching or any other processes now known or later developed.
FIG. 2A is top view of MEM actuator 200 according to one embodiment
of the invention. Actuator 200 is comprised of two coupled beams
201 and 202. In one embodiment, beams 201 and 202 may be
constructed of monolithic polysilicon. Metal layer 203 is bonded to
the top of beam 201. Metal layer 203 may be gold, nickel or any
other suitable material that has a higher thermal expansion
coefficient than the material used for beam 201.
FIG. 2B is a side view of MEM actuator 200 in an initial condition
200b, which is generally parallel to substrate 204. Actuator 200b
is held above substrate 204 by material 205, which may be the same
material as substrate 204 or beam 201, or may be constructed of
some other material. FIG. 2B represents an initial condition of the
actuator 200.
In FIG. 2C, actuator 200 has been heated, for example, by passing a
current through beams 201, 202 and layer 203. As a result of
heating, beams 201 and 202 have expanded. However, layer 203, which
has a higher thermal expansion coefficient than beam 201, has
expanded faster thereby forcing beam 201 to bend downward. Beam 201
is coupled to beam 202. Beam 202 consists of a single layer of
material. Accordingly, beam 202 expands under increased
temperature, but does not bend. However, because beam 202 is
coupled to beam 201, beam 202 is forced to rotate upward by angle
.theta., which corresponds to angle .theta. that beam 201 rotates
downward due to the asymmetric expansion of layers 203 and 201.
Angle .theta. increases as the thermal heating and expansion of
actuator 200 increases, until layer 203 reaches its yield point. If
layer 203 has exceeded its yield point, then, when actuator 200
cools and contracts, actuator 200 will assume new initial
configuration 200d illustrated in FIG. 2D. As discussed with
respect to FIG. 1C above, the residual stress in material 203
forces beam 201 to bend at the initial temperature. As a result, in
the new initial configuration, beam 202 is forced to rotate
downward by angle .phi..
It will be understood that if actuator 200d is heated, then beam
201 and layer 203 will again expand asymmetrically, thereby forcing
beam 202 to rotate upward from its new initial condition. In one
embodiment, actuator 200d can be heated so that beam 202 rotates up
to the original initial condition 200b. Actuator 200b represents
the original power-off condition of the actuator and actuator 200d
represents the modified power-off condition. As a result, after the
modification discussed herein, actuator 200 will assume
configuration 200d when no power or heat is applied to the system.
However, if a system requires that actuator 200 be in configuration
200b, then heat or power must be applied to the system.
A series of actuators, such as actuator 200, may be linked together
to form rotating and self erecting structures, such as those
exemplary structures illustrated in FIGS. 3A-C and 4.
For example, FIG. 3A is a rotary actuator 300 according to one
embodiment of the present invention. Actuator 300 is comprised of a
number of cascaded actuators 200 that are coupled to platform
301.
Rotary actuator 300 in FIG. 3A is in its initial power off
condition. When power is applied to actuator 300, each individual
bimorph actuator 200 activates and bends due to the asymmetric
expansion of beams 201 and 202. Because a number of bimorph
actuators 200 are linked together, the entire structure 300 is
forced to rotate so that platform 301 is rotated from the
horizontal plane into the vertical plane as illustrated in FIG.
3B.
If actuator 300 is heated sufficiently, layers 203 may exceed their
yield point as discussed above. As a result, when power is removed
and actuator 300 cools, it will not return to its initial state 300
shown in FIG. 3A, but will instead assume a new initial condition
300c illustrated in FIG. 3C. Accordingly, FIG. 3C represents the
new power off position for rotary actuator 300. When power is
applied, actuator 300 rotates to the new power on condition, which
corresponds to FIG. 3A.
In one embodiment, actuator 300 as manufactured looks like FIG. 3A.
Platform 301 may be a optoelectronic device, such as a mirror or
sensor. A beam of light, oriented as illustrated by arrow 302, may
pass across platform 301. When platform 301 is flat, as illustrated
in FIG. 3A, the light beam passes platform 301 without interruption
or detection. However, if platform 301 is elevated, as illustrated
FIGS. 3B or 3C, then the beam of light is detected, blocked and/or
reflected depending upon the type of device mounted on platform
301.
Depending upon the system, actuators having an initial condition as
shown in FIG. 3A or 3C may be appropriate. If it is desired to have
platform 301 in the path of light beam 302 as the default
condition, then actuator 300c should be used. Because actuator 300c
keeps platform 301 in the path of light beam 302 in the power off
condition, it will use less energy. When power is applied to
actuator 300c, it rotates to the position illustrated in FIG. 3A,
thereby allowing light beam 302 to pass unimpeded and
undetected.
However, if it is desired to allow light beam 302 to pass the
actuator so that platform 301 is only occasionally placed in the
path, then actuator 300a is desirable. Actuator 300a uses less
energy when platform 301 is in a retracted position relative to
light beam 302. When power is applied to actuator 300a, it rotates
upward to the position illustrated in FIG. 3B, thereby allowing
light beam 302 to hit platform 301.
One embodiment of the present invention is directed to a system and
method in which cascaded linear bimorph actuators achieve large
angle rotary displacements as illustrated in FIGS. 3A-C. Bimorph
units contain substantially parallel pairs of beams, including a
single material beam that remains straight when heated and a
bilayer beam that deflects when heated, due to differential thermal
expansion of the layers. In some embodiments, this concept is
applied as part of a unit cell. For a bilayer beam, advantageous
materials are gold on top of polysilicon. As the bilayer beam is
heated, the metal expands more than the polysilicon, producing a
deflection at the end of this beam. The angular deflection is
amplified by mechanically cascading interconnected unit cells in a
serpentine fashion. In some embodiments, successive beams are
connected electrically in series to provide a continuous current
path for resistive joule heating of the beams. This configuration
achieves cumulative rotational displacements up to greater than 90
degrees. In some embodiments, the actuator is fully released and
removed from the substrate to prevent mechanical interference
against the substrate when actuated. In other embodiments, at least
a segment of the substrate is removed from beneath the actuator to
prevent interference. In further embodiments, the actuator is
permanently anchored to the substrate.
In some embodiments, instead of having a physical axis of rotation
intersecting part of the actuator, where it could actuate and
interfere with the substrate, resulting in failure to rotate, the
actuator can instead rotate away from the plane of the substrate
about some virtual axis of rotation outside the actuator.
Embodiments of the present invention include single and plural-axis
rotary motion with anchored and releasable geometries. Potential
applications include rotary tweezers; Zero Insertion Force (ZIF)
connectors with large contact surface areas; micro-mirror scanning,
active optical alignment and beam steering, e.g., for telecom;
large angle optical scanners; endoscopy and micro-surgery; MEMS
manipulators; and any application in microsystems which requires
large angle rotation about an axis.
The rotary actuator embodiment illustrated in FIGS. 3A-C comprises
a plurality of cascaded coupled beams or actuators 200. Each of the
beams 200 have first arm 303 and second arm 304. The cascaded beams
may be disposed in a substantially planar folded serpentine array
structure, as illustrated in FIG. 3A, such that first arm 303 of
adjacent beam 200b is rigidly joined to second arm 304 of adjacent
beam 200a in the serpentine array structure 300a.
The first arm 303 (or 203 of FIG. 2A) of each beam 200 is operable
when activated to deflect or rotate in direction v out of the plane
of the original planar folded serpentine array structure 300a.
Second arm 304 of beams 200 is operable to remain undeflected when
actuator 300a is activated. Initial beam 200a and final beam 200d
in the serpentine array structure have terminal ends 305, 306,
respectively, that are not joined with an adjacent beam.
The folded serpentine array structure 300a is operable when
activated to rotate the final terminal end 306 relative to initial
terminal end 305 through an angle of rotation substantially
proportional to the sum of the deflections of all of said cascaded
coupled beams 200a-d in the folded serpentine array structure 300a.
The first arm 303 of beam 200b is a bimorph having an initial
configuration that is relatively flat as illustrated in FIG. 3A.
The configuration of first arm 303 is modified to a second
configuration when arm 303 heated beyond a yield point of the
materials 201, 203 comprising first arm 303.
Rotary actuator 300 of FIG. 3A may be rotated to any angle, such as
ninety degrees or beyond, as long as a sufficient number of beams
200 are used in the array. Rotary actuator 300 is capable of
erecting itself off of a substrate so that final terminal end 306
is lifted above the substrate. Final terminal end 306 may be
coupled to payload region 301 so that when actuator 300 is
operated, a payload on payload region 301 is rotated. Payload
region 301 is supported by two serpentine array structures. The
first array is comprised of beams 200a-d; and the second array is
comprised of beams 200e-h. A payload such as microcomponents,
mirrors, pick-and-place devices, rotary tweezers, mirrors, optical
alignment means, beam steering devices, optical scanning devices,
micro-surgical devices, microelectromechanical structure (MEMS)
manipulation devices and the like may be placed on payload region
301.
Payload region 301 may also be a microinductor in an Radio
Frequency (RF) circuit. The microinductor on payload region 301 may
be rotated away from a lossy substrate to improve RF performance of
the circuit.
Initial terminal end 305 may be attached to a substrate such as by
permanent anchoring or flexible tethering. In an alternative
embodiment, initial terminal end 305 may be releasably fastened to
the substrate. Although beams 200 and arms 303 and 304 are shown as
having substantially uniform length, it will be understood that
beams 200 and arms 303 and 304 may have varying or staggered
lengths in alternative embodiments.
Beams 200 may be thermally activated, for example, by using oven
heating, laser heating, conductive heating, resistive joule heating
and the like. Rotation of the actuator is caused by the bending of
arms 303 due to differential expansion of a bimorph. The bimorph
may be comprised of a metal and polysilicon. Beams 200a-h in the
serpentine array structures may be connected electrically in series
with one another to allow current to pass through the array
facilitating electrothermal heating. The serpentine array structure
300a may be electrothermally activated by passing electric current
in interwoven current paths through beams 200. In one embodiment,
the electrical currents in the serpentine array structures are
independently variable.
It will be understood that in alternative embodiments, beams 200
may be linked together in nonparallel formations thereby allowing
for actuators to provide more complex movements upon
activation.
FIG. 4 is a plan view depicting an alternative embodiment of the
present invention, using substantially the same unit cell concept
as in FIGS. 1A-2D. Structure 400 is a self-erecting structure that
is, in one embodiment, substantially flat having all components
substantially in one plane. When power is applied to self-erecting
structure 400, the beams of the structure bend thereby causing
payload area 401 to sink and/or rotate out of the initial plane
toward substrate 402.
For clarity, coordinate axes X, Y, and Z are shown in FIG. 4, with
the positive Z axis pointing out of the plane of the figure.
Substrate 402 lies substantially parallel to the X-Y plane.
Structure 400 is configured symmetrically in the X direction about
a Y-Z mirror plane midway between electrical contact pads 403 and
404. Accordingly, all elements described in the left portion of
FIG. 4 have mirrored counterpart elements with similar descriptions
in the right portion of FIG. 4.
In operation, electric current is applied between contact pads 403
and 404 to heat structure 400. Bilayer beam 405 has two layers
similar to bean 201/203 described above. In one embodiment, beam
405 is comprised of a monolithic polysilicon layer and a gold
layer. When heated, beam 405 bends downward (i.e. toward substrate
402) and when heated enough the gold will plastically deform. As a
result, when the power is removed, beam 405 assumes a new rest
position that is deflected out of the initial plane and rotated in
the positive Z axis (i.e. away from substrate 402). In a similar
fashion, beam 406 can be deformed to a new initial position that
mirrors beam 405.
Beams 407 and 408 are monolithic beams, such as monolithic
polysilicon, that remain substantially straight when heated.
Bilayer beam 405 is rigidly connected with single material beam 407
at their adjacent ends; and bilayer beam 406 is rigidly connected
with single material beam 408 at their adjacent ends. To prevent
structure 400 from mechanically interfering with substrate 402,
beams 407 and 408 may be made shorter than bilayer beams 405 and
406.
Connected with the far end of beams 407 and 408 are longer bilayer
beams 409 and 410 that, during operation (i.e. when heated), tend
to bend toward substrate 402 in the same manner as beams 405 and
406. Connected with the far end of beams 409 and 410 are
successive, alternating single layer and bilayer beams. Each
successive bilayer beam rotates toward substrate 402 when heated
and may be deformed to assume a new initial position that is
rotated away from substrate 402 in a power-off state. The
combination of the angular rotation and displacement of each
successive set of beams causes payload area to rotate toward
substrate 402 under power and to assume a deformed, at-rest
position rotated away from substrate 402.
The structure of FIG. 4 is anchored to substrate 402 at contact
pads 403, 404 and can accordingly self erect off of the substrate.
Structure 400 can be deformed to assume an at-rest or power-off
position wherein payload area 401 is rotated 90 degrees from the
initial X-Y plane. Accordingly, in a new power-off position,
payload area 401 may be substantially in the Z-X plane.
Alternatively, the structure of FIG. 4 can be flexibly tethered
either fully releasably or non-releasably to the substrate. A
releasable design would typically have a relatively simpler
actuation motion than that described in connection with FIG. 4.
In one embodiment, payload area 401 may be a capacitor plate and
structure 400 may be positioned to vary the capacitance in a
circuit. Alternatively, payload area 401 may be an inductor and
structure 400 may be positioned to minimize loss created by
coupling between the inductor and substrate 402.
It will be understood that, using the invention described herein,
structure 400 may be heated so that it is rotated out of the X-Y
plane to a point at which the stress in one or more of the
materials in the bimorph units, such as 409 or 410, increases
beyond the yield point. As a result, the bimorph unit will be
plastically deformed and, when the heat is removed, the bimorph is
forced to bend in the opposite direction as discussed herein. It is
expected that a corresponding or mirrored bimorph unit, such as
409' or 410', will also deform so that structure 400 remains
approximately symmetrical. In this exemplary embodiment, as a
result of the deformation, structure 400 assumes a new initial or
at-rest position in which it is rotated by some amount out of the
X-Y plain in the negative Z direction around the X-axis.
FIGS. 5A-C illustrate another microactuator according to an
alternate embodiment of the invention. In FIG. 5A, microactuator
500 has arm 501 that is a bimorph comprised of bonded materials 502
and 503. Preferably, material 502 has a higher thermal expansion
coefficient than material 503. Arm 501 is mounted on post 504,
which elevates the arm above substrate 505, thereby providing room
for arm 501 to move. Microdevice 506 is mounted on arm 501.
Microdevice 506 may be any device that may require small scale
adjustments to its position in a system. For example, microdevice
506 may be an optoelectronic receiver or transmitter that must be
positioned relative to a beam of light in an optical system.
Microactuator 500 in FIG. 5A is in an initial power off condition
with microdevice 506 at first position 50. When power is applied to
microactuator 500, such as when a current is applied to arm 501,
materials 502 and 503 heat up and expand. Due to the difference in
the materials' thermal expansion coefficients, arm 501 is forced to
bend downward as material 502 expands faster than material 503. As
a result, microdevice 506 is forced downward to new position 51 as
illustrated in FIG. 5B. Microdevice 506 position 51 is offset below
original position 50 (shown in outline in FIG. 5B).
It will be understood that if the power is maintained in the
system, then microdevice 506 can be kept at position 51. If
material 502 has not been pushed beyond its yield point and if the
power is removed from microactuator 500, then, as microactuator 500
cools, it will return to the original position illustrated in FIG.
5A and microdevice 506 will return to original position 50.
However, if sufficient heat is applied to material 502 in FIG. 5B
so that it is pushed beyond its yield point, then when power is
removed and microactuator 500 cools, it will assume the new
configuration illustrated in FIG. 5C. Residual stress in material
502 causes arm 501 to bend upward in a new power off configuration.
In this modified power off configuration, microdevice 506 is in new
position 52 that is above original position 50 (shown in outline in
FIG. 5C).
Position 52 is the new power off position for microdevice 506
following the plastic deformation of material 502. As a result,
microdevice 506 will remain in position 52 without requiring power
or heat to be applied to microactuator 500. Using the adjustments
illustrated in FIGS. 5A-C, the position of microdevice 506 can be
finely adjusted within a system. For example, if microdevice 506 is
an optoelectronic transmitter or receiver, its position may be
adjusted for alignment with other optoelectronic devices. Because
the power off position of the microactuator has been modified, the
system will use less power to keep microdevice 506 in a desired
position.
It will be understood that microdevice 506 may be moved from the
new power off position 52 by again applying power or heat to
microactuator 500. When power is applied, arm 501 is again forced
downward due to the asymmetrical expansion of materials 502 and
503. As a result, microdevice 506 may be moved from position 52 to
position 50 or 51 in a power on state.
FIG. 6 is a flowchart that illustrates the steps involved in
modifying a bimorph microactuator. In step 601 a bimorph
microactuator is manufactured. Such a microactuator may be, for
example, the type illustrated in FIGS. 2A-5C above or any other
microactuator in which a section of the microactuator comprises two
materials having different coefficients of thermal expansion. The
microactuator has an initial position.
In step 602 heat energy, such as an electrical current or a laser,
is applied to the bimorph actuator thereby causing the actuator to
bend due to the asymmetrical expansion of the bimorph. Heat energy
is applied until, in step 603, one of the bimorph materials is
pushed beyond a yield point. When the power or heat is removed in
step 604, the actuator assumes a new initial position due to
residual stress in one of the bimorph materials.
The new position can be adjusted by further stressing the bimorph
actuator under power. As the materials are pushed further beyond a
yield point, the new initial condition is moved farther from the
original position of the microactuator.
The electrothermal plastic deformation techniques disclosed herein
may also be used to assemble three dimensional (3D) structures. The
present invention can be used to create bi-directional actuators.
For example, a structure can be constructed using opposing sets of
actuators. The forces due to ambient temperature changes would
balance out in the structure, which would provide temperature
stability. Additionally, current or heat can be applied to either
beam independently to create unidirectional forces that will bend
the structure. The use of opposing beams in the microactuator
structure also allows for coarse positioning in one direction, with
fine adjustment in other direction.
Although the present invention and its advantages have been
described in detail, it should be understood that various changes,
substitutions and alterations can be made herein without departing
from the spirit and scope of the invention as defined by the
appended claims. Moreover, the scope of the present application is
not intended to be limited to the particular embodiments of the
process, machine, manufacture, composition of matter, means,
methods and steps described in the specification. As one of
ordinary skill in the art will readily appreciate from the
disclosure of the present invention, processes, machines,
manufacture, compositions of matter, means, methods, or steps,
presently existing or later to be developed that perform
substantially the same function or achieve substantially the same
result as the corresponding embodiments described herein may be
utilized according to the present invention. Accordingly, the
appended claims are intended to include within their scope such
processes, machines, manufacture, compositions of matter, means,
methods, or steps.
* * * * *